Airtight windows, energy-efficient appliances and low-flush toilets would all be mandatory in certain new private developments in the District under a bill that the D.C. Council is expected to pass Tuesday.

The anticipated vote would make the District the first major city in the United States to require private developers to make some new buildings efficient users of energy and friendly to the environment. A similar law was passed last week by the Montgomery County Council.

Features designed to save energy and protect the environment, such as the water-conserving toilets, can add 2 to 4 percent to the cost of construction, according to Natwar M. Gandhi, chief financial officer for the District, but other estimates reach 11 percent.

The features are among those that help projects comply with standards set by the nonprofit U.S. Green Building Council. The Green Building Act, to which the council is expected to give final approval Tuesday, would require most large construction projects in the city to the council's standards 2012. The law would apply to private buildings 50,000 square feet and larger and to all buildings that receive public financing of 20 percent or more. Mayor Anthony A. Williams (D) supports the measure.

In Montgomery, the legislation applies to public and private buildings larger than 10,000 square feet.

The District has six buildings certified as meeting Green Building Council standards, often known as LEED, short for Leadership Energy and Environmental Design.

The legislation follows a national trend of going "green," said Michelle Moore, vice president of communications and community for the Building Council. LEED standards have been approved in 18 states and 59 towns and counties, she said.

Six states, including Maryland, use building standards set by another nonprofit group, the Green Building Initiative.

Developers predict an explosion in the number of green buildings in the next few years. In the United States, 550 buildings have been certified as green by the D.C.-based Green Building Council, and more than 5,000 -- including Great Seneca Creek Elementary School in Germantown -- await certification.

Although Maryland allows builders to use the Green Building Initiative's standards, local jurisdictions can use others, and Montgomery will require those of the Green Building Council, said County Council President George L. Leventhal (D-At Large).

Enterprise Community Partners, a nonprofit group that advocates building green homes for low-income residents, is trying to ensure that affordable housing also meets LEED standards.

The group gave a $4.6 million grant to help renovate the 84-unit Galen Terrace in Southeast Washington. Residents have gone from apartments where cold air seeped in around the doors and windows to energy-efficient units. Renovation of all the units will be completed by April.

Tressa Weeks, 36, praised her new energy-efficient appliances and new windows. "The heat is better. The AC is better," she said.

The debate over the District's legislation placed the city in the midst of a nationwide competition between the Green Building Council and the Portland, Ore.-based Green Building Initiative, whose standards are called Green Globes.

Supporters of Green Globes tried to persuade Montgomery and District officials to include those standards in legislation, describing them as less expensive and able to give developers more flexibility.

Members of a D.C. Council task force on the issue recommended the LEED standards as stricter and entailing a more comprehensive certification process. The task force considered the Green Globes standards "to be a poison pill to the legislation," said Jim Graham (D-Ward 1), sponsor of the District's legislation.